Heat warning safety device for smooth cooktop stoves

ABSTRACT

Thermochromic compositions designed to turn red or orange and remain red or orange at or above a specified temperature, such as 115 degrees Fahrenheit, are shaped in the outline of the word “HOT” or in an outline of a ring interrupted by the word “HOT” and are embedded on the top surface of the heating element of smooth cooktop stoves or in certain embodiments on the window surface of wall ovens and toaster ovens so that they glow red or orange and instantly alert anyone that the heat element of the stove or the window is too hot to touch. For use on smooth cooktop stoves, including warming trays, the thermochromic display is embedded in a top surface of the smooth area of glass or metal that forms the heating element of the stove. For wall ovens and toaster ovens, the liquid crystals are embedded in the vertical window surface.

[0001] The present invention is a divisional application of and claimspriority from pending U.S. patent application Ser. No. 09/788,594entitled Heat Alert Safety Device for Smoothtop Stoves and Other HotSurface and filed on Feb. 21, 2001 by the same Inventor and Applicant asthe Inventor and Applicant herein, namely William S. Lerner. Thisapplication also claims priority from pending U.S. patent applicationSer. No. 10.238,348 filed Sep. 10, 2002 by Applicant Lerner.

FIELD OF THE INVENTION

[0002] The present invention relates to safety devices used in cookingor other activities involving hot surfaces and in particular it relatesto safety devices that alert someone that the surface of a stove orother appliance or device is too hot to touch. It also relates todetachable heat alert safety devices for any hot surface.

BACKGROUND OF THE INVENTION

[0003] With respect to stoves and related appliances, various kinds ofstoves—electric, gas, smooth cooktop using glass or metal tops—andtoaster ovens are well known to be used for heating food. In addition,“mobile stove-type appliances” such as hot plates and warming trays arewell known to be used for heating food. Each of these kinds of stovesand “mobile stove-type appliances” present a safety problem since theheating elements of the stove are hot during the cooking process andremain hot well afterwards. During the cooking process, the safetyproblem caused by touching the heating element is mitigated somewhat byvisual inspection of the stove. With a gas, electric or smooth topstove, for example, the presence of a pot or other utensil on top of thestove might alert someone to the fact that the stove appears to be inuse for cooking and therefore too hot to touch. Even the presence of apot or other utensil is not a reliable clue, however, since people tendto leave tea kettles on their stove perpetually. When the cookingprocess has ended, however, it is generally impossible to detect thatthe heating elements of the stove remains hot and would burn the skin ofanyone who touched them. There is no visual or other clue that the stoveis hot.

[0004] To some degree, adults have developed an inherent caution whenapproaching stoves because of their experience and knowledge in dealingwith such safety problems. This inherent caution, however, does notobviate the need for a device that warns the adult when touching thestove would be dangerous. Moreover, children, and particularly youngchildren, usually have not developed such a watchfulness and there haslong been a need for a device that can prevent burn accidents tochildren who may inadvertently touch a stove that is hot, especiallywhen the stove remains hot well after the cooking process has ended.

[0005] Furthermore, the reduction in the size of modern kitchens has ledthe occupants of modern apartments to make use of the stove as anextension of the counter top adjacent the stove as a resting places forlarge items that have been carried into the kitchen area. An example ofsuch items is heavy bags of groceries brought into the kitchen. There isan urge to set the bags down on the nearest flat surfaces, which may bethe top of a stove adjacent a counter top. This is particularly true forthose stoves that are smooth on top, such as smooth cooktops. Ingeneral, the top surfaces of modern kitchen stoves are increasinglyflat, especially the top surfaces of smooth cooktops. These factors haveonly increased the danger to adults when the top surfaces of stoves areused as a resting place for packages, such as groceries brought into thekitchen.

[0006] Smooth cooktop stoves presently are also dangerous if touched ontheir top surface when they are still hot, even after use. These smoothcooktop stoves, or “smoothtops” as they are sometimes called, utilize asthe heating element separate areas on the top surface of the stove (atthe same location that gas stove would have burners) which are made ofglass. Under each area, usually circular, is a strong light source, suchas a halogen lights. The light source projects the light upward to thesurface area of the smoothtop's heating element—the glass area on thetop surface of the stove. Since the glass area is coated on its bottomwith a dark coating, when the light strikes it, the heat from the stronglight is absorbed by the glass area and these glass surfaces form eachheating element of the stove.

[0007] Another variation of the smooth cooktop is the use of a “ribbonheating element” where the smooth glass surface is heated by a coiledelectric circuit called a “ribbon element” just underneath it instead ofby a halogen light source. The heat is transmitted directly upward sothat only the heat element itself gets hot and the rest of the cooktopsurface remains cool. In some cases, the ribbon heating element also hasanother feature whereby the heating element is made of two concentriccircles so that the option exists of two sizes of the heating element tomatch the two different sizes of the pans that need to be heated. Thisnew technology does not solve the problem of warning adults and childrenthat the heating element should not be touched when the cooking processhas ended. If anything, it generates the additional hazard that someonecan be lulled into touching the heating element after thinking theheating element is cool since the surface right adjacent to it is indeedcool.

[0008] With respect to toaster ovens, because of its mobility the dangerof touching the window of a toaster oven exceeds that of the typicalimmobile oven. The toaster oven can be placed on a counter top or otherportion of the kitchen not directly in the “cooking center”.Consequently, an adult and especially a child, or the elderly, is notlikely to remember not to touch a window of a toaster oven when it isoff (soon after it had been on). In addition, the door of a toaster ovencan be left open and jut out further toward someone in the kitchen.

[0009] Presently, in order to address the danger of touching a hot“smoothtop” stove, such stoves generally have several light indicators,each one corresponding to each heating element, all located in small onerectangular area on the surface of the cooktop. The light indicatorsremain lit for a certain length of time after the stove's heatingelement is turned off in order to deter someone from touching theheating element when it is still hot, although “off”. Unfortunately,this attempt to address the danger of touching a hot stove of the smoothcooktop variety is insufficient as a warning system (putting aside thefact that the light indicators are designed only for the smooth cooktopvariety stoves to begin with and not for gas and electric coil stoves).

[0010] A quick glance at the group of light indicators would not besufficient to warn the average adult, no less children or the elderly,that a particular heating element is too hot. This is because the groupof light indicators do not immediately tell someone which heatingelements correspond to which light indicators. At a minimum, severalseconds of concentration are needed in order to determine from the lightindicators that are “on”, which heating elements are too hot to touch.Most adults, and certainly most children, cannot afford those seconds ofdeduction since their desire to touch the stove is immediate. Inaddition, an adult carrying groceries into the kitchen and looking for acounter top to place them on or a child running into and playing in thekitchen are even less likely than the average adult or child to take thetime to engage in a several second thinking process. Accordingly, thechild or the adult will be inadequately warned about the danger of beingburned. With this in mind, it is no surprise that a 1997 industrialdesign exhibit at the Cooper Hewitt (Smithsonian) in New Yorkdemonstrated that over 69% of adults can not match the control knob withits corresponding burner (i.e. heating element) on a stove.

[0011] There is also not presently known any effective warning methodfor the vertical surfaces of oven windows, including the windows of wallovens, regular ovens and toaster ovens. This is particularly importantsince when the oven is turned off, the oven window remains very hot eventhough it appears that everything is off.

[0012] In addition, while devices that make use of liquid crystalcompositions are known to indicate the surface temperature of anappliance, these devices are not designed to warn someone of the dangerof touching hot stoves. For example, U.S. Pat. No. 3,827,301 to Parkerdiscloses an apparatus for indicating the temperature of a surface of anappliance. It has a first portion in contact with the appliance surfaceor connected by copper wires or heat pipes to the appliance surface. Ithas a second portion, a poor heat conducting member in heat exchangingrelationship to the ambient environment, that has bands of liquidcrystal material extending away from the first portion thereby creatinga temperature gradient extending away from the surface of the appliance.

[0013] Devices such as disclosed in Parker that provide temperaturedeterminations are not adequate for instantly warning a child or even anadult that the heating element of a stove is too hot to touch for onething because quantitative temperature determinations are inadequate toprovide the immediate warning that is necessary. Moreover, the device ofParker and other liquid crystal compositions are not specifically suitedto be manufactured as part of a stove. In addition, these devices arenot suitable as attachments to stoves and certainly not as attachmentsto a smooth cooktop stove.

[0014] The present invention is also applicable, not just to stoves andrelated appliances, but to any other surface that one may need to bewarned that it is hot. There are numerous devices whose surfaces becomehot and remain hot even after the device has been shut off eitherelectrically or otherwise. For example, a radiator cap becomes hot whenthe vehicle and radiator shut off. Also, any kind of piping that is aconduit for hot liquids is an example of a surface that one may need tobe warned that it is hot. Other devices having hot surfaces include hotsurfaces on fireplace doors, radiator caps, irons, chafing dishes,coffee urns, heating pipes, home radiators, glue guns, oven doors,portable heaters of electric, oil and ceramic disc, kerosene lamps,kerosene heaters, barbecue grills of electric, gas or coal, electricwoks, electric skillets, deep fryers for home or commercial use, heatlamps in self service cafeterias and salad bars, saunas including themetal box that generates and/or controls the heat, rotisseries, indoorgrills whether gas or electric, tea kettles, wood burning stoves, hotelectric rollers, hot wax holders used for beauty treatments, bonnettype hair dryers, curling irons, portable generators, steam cleanersespecially such as in dry cleaning facilities, hot water pipes that areexposed, hot water heaters, furnaces, warming trays, light fixtures suchas halogen lamps, popcorn makers (especially commercial ones), toasters,cappucino and espresso makers, autoclaves used to sterilize instrumentsin a medical setting, movie projectors and other such hot surfaces.These and other hot surfaces are exposed to children, maintenance worksand ordinary adult users.

[0015] Accordingly, there is needed a versatile, easily movable andmountable, removably attachable and detachable, and effective,convenient and easy to manufacture device for warning adults, workersand children instantly when any kind of surface, whether it be a stoveof any kind or any other surface, is too hot to touch. There is also aneed for such a device that is both capable of installation on apreviously purchased stove of any known type, including cooktops,electric and gas stoves, and one that is also capable of beingmanufactured as part of the stove by stove manufacturers. The presentinvention addresses and satisfies all of these needs and provides otheradvantages.

[0016] There is also a need for an effective, convenient and east to useand detachable heat alert safety device that is easily read andunderstood for warning adults and children when any surface is too hotto touch. Such a device should ideally be positionable at a variety ofheights or positions so that it can be custom tailored for children ofdifferent height.

[0017] Importantly, moreover, there is a need for a heat alert safetydevice that is versatile enough to be easily positioned on a hot surfaceand yet be able to be easily removed thereafter when it has served itspurpose—either with respect to that surface or it has served its purposewith respect to that particular individual or it has served its purposefor that individual for that particular moment—and then be repositionedelsewhere—either on another hot surface of another object or anothersurface of the same object or even another portion of the same surfaceof the same appliance. This is necessary because in order for the heatalert safety device of the present invention to be effective it has tobe visible (or at least discernable) and in addition it should bediscernable and effective for children; and since children of differentages are of different heights it is advantageous to be able to attachthe device to. It is also necessary because a particular individual maydecide to relocate the heat alert safety device when a differentappliance is used or when a different portion of a kitchen counter isused, or when any other object with a hot surface is activated. Itshould be noted that by “activated” is included situations when anobject is “hot” a certain amount of time after the source of the heatwas “on” and it is of course not intended that the device of the presentinvention is limited to situations when electricity is “on” for anappliance or other object.

SUMMARY OF THE INVENTION

[0018] In the present invention, liquid crystal compositions that changecolor and remain at that color when they reach or exceed a certaintemperature (referred to generally herein as “liquid crystalcompositions”), such as cholesteric liquid crystals or various types ofliquid crystal polymers designed to turn color when they reach a certaintemperature, and that are shaped in the outline of the word “HOT” areembedded in a device attachable to or forming a part of any hot surfacesuch as the top surface of the heating element of stoves so that theyglow red and instantly alert anyone, including a child, that the heatingelement of the stove is too hot to touch even when the stove or otherdevice is “off”. In one embodiment described and claimed in my previouspatent, U.S. Pat. No. 6,104,007, for use on electric stoves, the deviceis an improved electric coil whose central area contains the liquidcrystals. In a second embodiment for use on smooth cooktop stoves, wallovens and toaster ovens, the liquid crystal display is embedded in theglass areas that form the heating elements of the smooth cooktop stove.As an alternative to the second embodiment, for smooth cooktop stoves,the liquid crystal display is in the shape of a ring surrounding theheating element (and visible when pots are placed on the heatingelement) which ring may have an interrupted area in the outline of theletters “HOT”). In a third embodiment for gas stoves also described andclaimed in U.S. Pat. No. 6,104,007, the liquid crystals are embedded ina recessed disk mounted on top of the central element of the gas stove'sburner. In each embodiment, the liquid crystals stay red as long as thetemperature they sense exceeds a certain degree Fahrenheit, such as 115degrees Fahrenheit, which has been found to be too hot to touch. In afourth embodiment for use on wall ovens and toaster ovens, the liquidcrystal display is embedded in the glass areas that form the heatingelements of the smooth cooktop stove.

[0019] In one embodiment described in detail herein, in order tooachieve removable attachability and placement, the heat alert safetydevice is made of two part, a half-dollar disk made of Pyrex andcontaining the liquid crystal composition and an attachment and heatconducting element in a disk in the shape of a dime on the back of thehalf-dollar shaped disk.

OBJECTS AND ADVANTAGES

[0020] The following important objects and advantages of the presentinvention are:

[0021] (a) to provide a device that instantly warns anyone including achild that the surface of a stove, hot plate, the window of a toasteroven, or other hot surface is too hot to touch,

[0022] (b) to provide a device that instantly displays to anyone theletters “HOT” as a warning on the surface of a stove,

[0023] (c) to provide a device that instantly provides a warning displayto anyone using the letters “HOT” that appears directly on the heatingelement of the stove surface so that it is clear to anyone what is toohot to touch,

[0024] (d) to provide a versatile heat warning device that can be usedfor smooth cooktop stoves having any kind of surface including glass ormetal and using any kind of technology including electric heating,electric induction and halogen light heating, or can be used forelectric stoves, or for gas stoves, for wall ovens, for toaster ovens,for hot plates or for warming trays,

[0025] (e) to provide a device for smooth cooktop stoves having any kindof surface including glass or metal and using any kind of heatingtechnology including electric heating, electric induction and halogenlight heating that instantly displays to anyone as a warning on thesurface of the stove a ring surrounding each heating element of thestove, which ring may contain in an interrupted area of the ring theletters “HOT”, the ring and letters turning red at a certain temperatureof the heating element,

[0026] (f) to provide a heat warning device that is easy to manufactureand that can be either installed onto the stove (or other appliance's)heating element or can be manufactured as part of the stove,

[0027] (g) to provide a heat warning device for stoves that can becalibrated to signal the word “HOT” or in the case of cooktop stoves tolight up a ring around the heating element only when a certaintemperature, such as 115 degrees Fahrenheit, is reached and that canremain in signaling mode as long as such temperature is exceeded by theappliance surface,

[0028] (h) to provide a heat warning device as above that makes use ofliquid crystals that change color when a certain temperature is reached,such as cholesteric liquid crystals or various types of liquid crystalpolymers designed to change color when a certain temperature is reached,

[0029] (i) to provide a heat warning device that is removably attachableto a wide variety of hot surfaces in a very simple manner,

[0030] (j) to provide a heat warning device that can is readable bychildren and whose placement can be adjusted when the child growstaller,

[0031] (k) to provide such a heat warning device that can be angled foreasier reading on surfaces in out-of-the-way locations such as pipes,

[0032] (l) to provide such a heat warning device that contains a magnetor an electrically conductive plastic that makes the device removablyattachable to any hot metal, glass or other suitable surface and capableof receiving heat transmitted from the hot surface and transferring itto the liquid crystals that change color when a certain temperature isreached and

[0033] (m) to provide a heat alert safety device that is readilyattachable to and detachable from hot surfaces on fireplace doors,radiator caps, irons, chafing dishes, coffee urns, heating pipes, homeradiators, glue guns, oven doors, portable heaters of electric, oil andceramic disc, kerosene lamps, kerosene heaters, barbecue grills ofelectric, gas or coal, electric woks, electric skillets, deep fryers forhome or commercial use, heat lamps in self service cafeterias and saladbars, saunas including the metal box that generates and/or controls theheat, rotisseries, indoor grills whether gas or electric, tea kettles,wood burning stoves, hot electric rollers, hot wax holders used forbeauty treatments, bonnet type hair dryers, curling irons, portablegenerators, steam cleaners especially such as in dry cleaningfacilities, hot water pipes that are exposed, hot water heaters,furnaces, warming trays, light fixtures such as halogen lamps, popcornmakers (especially commercial ones), toasters, cappucino and espressomakers, autoclaves used to sterilize instruments in a medical setting,movie projectors and other such hot surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a top plan view of a gas stove having the device of thepresent invention on each burner.

[0035]FIG. 2 is an enlarged fragmentary plan view of a heating elementof a gas stove having the device of the present invention.

[0036]FIG. 3 is an enlarged fragmentary cross-sectional view taken alongline 3-3 of FIG. 2.

[0037]FIG. 4 is the prior art smooth cook top stove showing lightindicators.

[0038]FIG. 5 is a top plan view of the device of the present inventionused on an electric stove.

[0039]FIG. 6 is an enlarged fragmentary plan view of one heating elementof an electric stove having the device of the present invention.

[0040]FIG. 7 is an enlarged fragmentary cross-sectional view taken alongline 7-7 of FIG. 6.

[0041]FIG. 8 is a top plan view of the device of the present inventionon the smooth surface of a cook top stove.

[0042]FIG. 9 is an enlarged fragmentary plan view of one heating elementof a smooth cook top stove having the device of the present invention.

[0043]FIG. 9A is an enlarged fragmentary plan view of one heatingelement of a smooth cook top stove and having the device of the presentinvention in the shape of a ring surrounding the heating element.

[0044]FIG. 10 is a enlarged fragmentary cross-sectional view taken alongline 10-10 of FIG. 9.

[0045]FIG. 10A is a enlarged fragmentary cross-sectional view takenalong line 10A-10A of FIG. 9A.

[0046]FIG. 11 is a front elevational view of a wall stove having thedevice of the present invention.

[0047]FIG. 12 is an enlarged fragmentary front elevational view of oneheating element of a smooth cook top stove having the device of thepresent invention.

[0048]FIG. 13 is a enlarged fragmentary cross-sectional view taken alongline 13-13 of FIG. 12.

[0049]FIG. 14 is a front elevational view of a wall oven having thedevice of the present invention.

[0050]FIG. 15A is a side view of an alternative embodiment of the deviceof the present invention.

[0051]FIG. 15B is a front view of an alternative embodiment of thedevice of the present invention.

[0052]FIG. 16A is a side view of an alternative embodiment of the deviceof the present invention.

[0053]FIG. 16B is a front view of an alternative embodiment of thedevice of the present invention.

[0054]FIG. 17A is a side view of an alternative embodiment of the deviceof the present invention.

[0055]FIG. 17B is a front view of an alternative embodiment of thedevice of the present invention.

[0056]FIG. 18A is a side view of an alternative embodiment of the deviceof the present invention for attaching to rounded hot surfaces.

[0057]FIG. 18B is a side view of an additional alternative embodiment ofthe device of the present invention for attaching to rounded hotsurfaces.

[0058]FIG. 19 is an alternative embodiment of the device of FIG. 16Athat can be positioned at different angles.

[0059]FIG. 20A is an alternative embodiment of the device of FIG. 15Aincluding a straight face.

[0060]FIG. 20B is an alternative embodiment of the device of FIG. 16Aincluding a straight face.

DETAILED DESCRIPTION OF THE DRAWINGS

[0061] One of the embodiments of the present invention, as described andclaimed in my previous patent, U.S. Pat. No. 6,104,007, is for stovesthat employ gas heat, as seen in FIGS. 1-3. In this embodiment, the topof the stove 100 typically has four heating elements 7, that are calledburners and that are covered by metal grates 9, that are open in themiddle. Each burner or heating element is situated in a recessed area 8and is surrounded by the metal grate. As best seen in FIG. 2, there is acentral metal element 10 in which a series of gas inlet holes on theside 10 a of the central metal element permit gas to flow through andignite. As seen in FIGS. 1-3, the central metal element 10 has a disk 12on a top surface 12 a of the central metal element 10 and this disk 12contains liquid crystals 14 in the form of the letters “HOT” that changecolor when they reach a certain temperature. Alternatively, the centralmetal element 10 itself can have embedded therein on its top surface theliquid crystals 14 in the shape of the letters “HOT” using knownmethods.

[0062] The temperature of the grates upon which pots and pans restduring cooking may be roughly equal to the temperature of the centralmetal element 10. Accordingly, whenever the letters “HOT” become redboth the grates and the central metal element may be too hot to touch.However, there may be some discrepancy between the temperature of thegrates and that of the central metal element 10. To take into accountany discrepancy between the temperature at which the central element 10becomes cool and the temperature at which the metal grates become coolenough for safe touch, the turning temperature, as an option, thetemperature at which the liquid crystal compositions 14 (such ascholesteric liquid crystals or various types of liquid crystal polymersdesigned to turn red at a specific temperature) turn red, can becalibrated by lowering the turning temperature by an estimate of theamount of this discrepancy so that if either the grates or the centralmetal element 10 is too hot the liquid crystals 14 will remain red.

[0063] FIGS. 5-7 depict an embodiment of the present invention describedand claimed in my previous patent, U.S. Pat. No. 6,104,007, for the topsurface of electric stoves. Electric stoves typically have four heatingelements on the top of the stove made of electric coils 20 wound in aserpentine configuration and sitting on a metal rest 21. Normally,electric coils 20 have a recessed disk 22 in a central area of each coil20 that is connected to and held up by the metal rest 21. FIGS. 5 showstop plan view and FIG. 6 shows an enlarged fragmentary plan view ofelectric coil 20 of the present invention having central disk 22containing liquid crystal compositions 24 (which may be cholestericliquid crystals or various types of liquid crystal polymers designed toturn color at a specific temperature) that are in the shape of theletters “HOT” embedded on the top surface 22 a thereof. The liquidcrystals 24 become red whenever the temperature of central disk 22exceeds 115 degrees Fahrenheit and remains red unless and until thistemperature is crossed again. This electric coil 20 may be made byembedding the liquid crystals 24 on the top surface 22 a of the centraldisk 22 using methods well known in the art. Alternatively, existingelectric coils can be modified by fitting thereon a disk containing onits top surface liquid crystals 24 embedded therein.

[0064] The central disk 22 containing liquid crystals 24 in the shape ofthe letters “HOT” embedded on the top surface 22 a is recessed roughly aquarter of an inch below the surface of the electric coil 20 so thatwhen pans and pots are placed on the electric coils they do not scratchthe central disk 22.

[0065] As an option, since there may be some discrepancy between thetemperature of the electric coil 20 and that of the central disk 22, theturning temperature at which the liquid crystals 24 turn red, can be setto be the lower of (i) the temperature of the electric coil 20 and (ii)the temperature of the central disk 22. This way, someone is warnedagainst touching either the central element 22 or the actual coil 20.

[0066] FIGS. 8-10 depict an embodiment of the present invention for usewith smooth cooktop stoves, sometimes called “smoothtops” or “cooktops”.For cook top stoves, the prior art is shown in FIG. 4. As seen in FIGS.8-10, smooth cooktop stoves have heating elements that consistessentially of an area of glass surface 30 that is smooth on top andwhose underside is made dark enough to absorb light. Such absorptiongenerates heat in the smooth area of glass 30. Underneath each area 30,usually circular, is a strong light source 36, such as a halogen lights.The light source 36, as seen in FIG. 10, projects the light upward tothe surface area of the smoothtop's heating element—the glass area 30 onthe top surface of the stove. Since each glass area is coated on itsbottom with a dark coating, when the light strikes it, the heat from thestrong light is absorbed by the darkened portion of the smooth area ofglass 30. These glass surfaces 30 form the heating elements of thestove. For cooking, cooking utensils are simply placed over the area(which may be square, round, etc.) of the heating element on the glasssurface. Some smooth cooktop stoves employ. “radiant” heat sources forthe glass areas instead of halogen light sources 36 but the effect isthe same. In addition, some smooth cooktop stoves have halogen lamps(under each area 30 as before) but they emit infrared waves that providelight and heat.

[0067] The heat alert device of the present invention when used for thesmooth surface of cooktop stoves of either type would comprise liquidcrystal composition 32 embedded in the top surface of each glass area30, which is the heating element on the smooth cooktop stove using knownmethods. For example, the liquid crystal composition 32 may be made inthe exact shape of the letters “HOT” by spraying the composition ofliquid crystals 32 over each glass area 30 after covering the glass area30 with a cardboard stencil or other cut-out in the outline or shape ofthe letters “HOT”. As before, the liquid crystal composition is designedto turn red and remain red whenever the temperature of the smooth areaof glass exceeds a specified temperature, such as 115 degreesFahrenheit.

[0068] As an alternative to the second embodiment, for smooth cooktopstoves using any technology including electric heating, electricinduction and halogen light heating, the liquid crystal display is inthe shape of a ring surrounding the heating element (and visible whenpots are placed on the heating element) which ring may have aninterrupted area in the outline of the letters “HOT”, as seen in FIGS.9A and 10A. This addresses and solves the problem that people oftenleave pots or kettles on the stove perpetually and that with cooktopstoves the result of doing so is that the heating element is no nevervisible (since the pot or kettle may be as large or large than theheating element). In such situations, no matter how mature, cautious andalert you are, you cannot readily ascertain that the heating element(and the kettle or pot above it) is too hot to touch. By seeing the ringof the present invention (with or without the letters “HOT” filling aninterrupted portion thereof) lit up as red, you immediately know thatthe area of the heating element is too hot to touch. In this embodiment,the liquid crystal composition 32 is embedded on the stove surface inthe outline of a ring (and in the letters “HOT”) in a location ofsurrounding the heating element, i.e. surrounding the top surface of thesmooth glass or metal areas 30 on the stove surface 31.

[0069] Although FIGS. 8-10 (including FIGS. 9A, 10A) have been describedin terms of smoothtops with heating elements made of smooth glasssurfaces, other variations of smooth top stoves exist—in particularsmooth metal tops called electric cooktops. The difference is that alight source 36 would not be used under the surface to generateheat—instead the metal gets hot by being connected to a heat source thatmay be electric (not shown). In addition, some smooth cooktops use a“ribbon heating element” instead of halogen light sources where thesmooth glass surface is heated by a coiled electric circuit called a“ribbon element” directly and immediately underneath the glass insteadof by a halogen light source. The device of the present invention worksthe same way for metal cooktops, glass cooktops and for those that relyon halogen light source as the heat or those that use ribbon heatingelements. FIGS. 8-9 which depicts the present invention for use withglass cooktops also depicts the present invention as applied to smoothmetal cooktop stoves and as applied to ribbon heating elements. FIG. 10,which describes the present invention for use with glass cooktops thatemploy halogen light sources, the top part of FIG. 10 also depicts across section of the liquid crystal composition for smoothtops—for metalcooktops and glass cooktops using ribbon heating elements the halogenlight source 36 would not be present but everything else would be thesame. For all of the smooth cooktops, the liquid crystal composition 32would still be embedded in the top surface of the smooth metal areas 30on the stove surface in the shape of the letters “HOT”.

[0070] Other variations of smooth cooktops also exist and the liquidcrystal composition in the shape of the letters “HOT” can also beembedded in their surfaces. For example, some smooth cooktops have araised solid element having a smooth top and made of metal having arecessed central area. The liquid crystal composition would be embeddedin this recessed central area as before in the shape of the letters“HOT”.

[0071] FIGS. 11-13 depict a wall oven whose window surface 40 hasembedded thereon the liquid crystal composition 46 of the presentinvention in the shape of the letters “HOT”. As before, the liquidcrystal composition 46 is designed to turn red and remain red wheneverthe temperature of the smooth area of glass exceeds a specifiedtemperature, such as 115 degrees Fahrenheit. The purpose is to warnchildren or adults not to touch the surface of the window 40 that getsvery hot when the oven is on. There is not present a convenient andeffective warning method in use for the vertical surfaces of ovenwindows. This is particularly important since when the oven is turnedoff, the window 40 remains hot even though it appears that everything isoff.

[0072] Toaster ovens also have a window surface 40 which would haveembedded thereon the liquid crystal composition 46 of the presentinvention in the shape of the letters “HOT”. As before, the liquidcrystal composition 46 is designed to turn red and remain red wheneverthe temperature of the smooth area of glass exceeds a specifiedtemperature, such as 115 degrees Fahrenheit.

[0073] Hot plates can be thought of as small mobile electric stoveshaving one heating element. Warming trays can be thought of as smallmobile smooth cooktop ovens having one smooth surface as a heatingelement. In both of these cases, the hot plate and the warming tray, thepresent invention would be applied to the heating element and functionthe same way as described with respect to their larger and morepermanent counterparts—the electric stove and the cooktop stove.

[0074] It should be noted in general that the present invention makesuse of any liquid crystal composition that changes color and remains atthat color when a specified temperature is reached or exceeded—it neednot necessarily be cholesteric, although it has been found thatcholesteric liquid crystals do this effectively. It is also within thescope of the present invention to make use of a liquid crystalcomposition that changed color when it reached a specified temperatureor temperature range but changed to a third color at a higher thresholdtemperature, so long as the third color is significantly different fromthe first color—although this would certainly not be the ideal kind ofliquid crystal composition. The ideal composition turns red at aspecified temperature and remains red above that temperature.

[0075] With use of the present invention, when an individual enters thekitchen with the cook top stove in it he or she can instantly recognizeif any of the heating elements are too hot. This is in contrast to theprior art for which the person would have to first figure out whichheating element corresponds to which light indicator.

[0076] The present invention contemplates that other letters and otherletter shapes besides that of “HOT” could be used as a warning althoughit is believed that the simple arrangement of the letters “HOT” in thesimplest typeset provide the best warning. Furthermore, the presentinvention also contemplates that the liquid crystal composition in theoutline of the letters “HOT” can be embedded in a surface of a stove,toaster oven or other appliance where the surface is vertical andperpendicular to the floor, not only horizontal. In addition, while thedrawings depict the liquid crystal composition embedded on the surfaceof the stove in a particular configuration and depth, it is contemplatedby the present invention that the depth and configuration of the liquidcrystal composition can vary and still be within the scope of thisinvention.

[0077] It is also contemplated by the present invention that glass diskscontaining liquid crystal compositions in the shape of the letters “HOT”can be made so as to be purchased separately by the consumer as a glassdisk having embedded therein the liquid crystal composition to beaffixed to a glass surface area of a cooktop stove, a wall oven or atoaster oven.

[0078] It is also contemplated by the present invention with respect toall embodiments that in addition to the liquid crystal composition beingin an outline of the letters “HOT”, the liquid crystal composition couldinstead be in the background of such an outline. By this is meant thatthe liquid crystal composition would form the entire area except anoutline of the letters “HOT”. The point of one feature of the presentinvention is to use the liquid crystal composition to create a colorcontrast between red and some other color in order to depict the letters“HOT” in red whether by virtue of the liquid crystal composition itselfbeing the letters “HOT” or whether the liquid crystal compositionsurrounds the letters and in effect constitutes everything else exceptthe letters “HOT”. Furthermore, it should be noted that in this patentapplication, the term “red” refers to all possible variations and shadesof the color red as well as to all possible variations of the colororange. Red and orange are the colors associated with heat. Furthermore,if the hot surface (as opposed to the area of the liquid crystalcomposition) itself is or becomes red when hot, then the liquid crystalcomposition 230 would have to be orange and vice versa.

[0079] In all embodiments of the present invention it is contemplatedusing the thermochromic composition to form the heat warning symbol, forexample the letters “HOT”, by undergoing and maintaining a readilyperceptible color change whenever a specified temperature is exceeded.Accordingly, turning red or orange are merely examples of such a colorchange.

[0080] The term thermochromic composition refers to compositions such asliquid crystal compositions that change color and remain at that colorwhen a certain temperature is exceeded.

[0081]FIGS. 15 through 20 depict several alternative shapes for aversatile heat alert safety device 200 of the present invention. Theversatile heat alert safety device of the present invention is designedto address many of the needs outlined, including the need for a devicethat can be attached to a hot surface and later removed and re-attachedeither to a different hot surface or a different part of the same hotsurface. The hot surfaces are typically metal or glass but can be ofother suitable materials. In each of the shapes shown in FIGS. 15-20,the device is essentially comprised of two parts, an attachment part anda container part having the liquid crystal composition, each of which isadjacent to the other. In some cases, the parts are attached like a dimeaffixed adhesively to the back of a half-dollar (of U.S. currency). Itshould be noted that for the embodiments depicted in FIGS. 15-20 theoverall device of the present invention has been assigned the referencenumeral “200”.

[0082] As seen in FIGS. 15A and 15B, the first part of device 200 is theattachment element 220 that is a thin disk that may be round or square.Attachment element 220, which is attached to the metal or glass surface(not shown), conducts heat. Attachment element 220 may be either amagnet or else an electrically conductive plastic. Such electricallyconducting plastic would also either have adhering characteristics sothat device 200 that are sufficiently strong to adhere the device 200 tothe hot surface but sufficiently weak so that the device 200 can beremoved from and hence be removably attached to the hot surface.Alternatively, the heat conducting plastic would have a layer of weaklyadhering plastic of any kind at a rear surface that comes into contactwith the hot metal, glass or other surface. Plastics made of polymersthat conduct electricity and transmit heat are known to organicchemists. This attachment element 220 makes the device 200 removablyattachable to virtually any hot surface.

[0083] The second part of device 200 is composed of the liquid crystalcomposition 230 itself and a container 240 for containing these crystals230. Ideally, curved face 242 of container 240 is convex and curvedalthough typically not rounded to the extent of being a hemisphere sinceif the container 240 had too much of a height it would limit the rangeof angles from which the letters “HOT” on curved face 242 can be seen.Alternatively, and less ideally, straight face 242 a of container 240 amay be used, as seen in FIG. 20. Container 240 is also somewhat diskshaped in that it has a flat rear edge 247 (like the flat side of ahemisphere) that attaches to the flat container attachment side 220 b ofthe attachment element 220. Typically, although not necessarily,container 240 has a larger diameter than the diameter of the attachmentelement 220 because the diameter of container 240 should reflect thefact that it is desirable that the letters “HOT” on curved face 242 bewidely visible while the diameter of attachment element 220 need only belarge enough to yield a secure attachment of device 200 to the hotsurface.

[0084] Container 240 is made of a heat transmitting substance capable ofbeing transparent such as any of a variety of heat conducting glasswareproducts sold under the name “Pyrex” or any heat transmitting plasticthat is capable of being transparent. Curved face 242 of container 240is transparent at least in the portion of curved face 242 that coversthe liquid crystal composition 230. Accordingly, curved face 242displays the letters “HOT” when the surface to which the heattransmission element 220 is attached exceeds a specified temperature,for example a temperature above approximately 115 degrees Fahrenheit.

[0085] The attachment element 220 of device 200 has a flat containerattachment side 220 b that is attached to the flat rear edge 249 of thecontainer 240 by a variety of means, such as by epoxy or by being weldedif the heat attachment element is 220 is a magnet. The epoxy should ofcourse not be so extensive that it impedes the heat transmission betweenthe two parts of device 200.

[0086] As seen in FIGS. 16A and 16B, an alternative shape of device 200includes what is called a mushroom shaped container 340 composed of astem 345 and a convex face 346. Typically, and this is why it isreferred to herein as “mushroom shaped”, stem 345 is narrower indiameter than convex face 346 although it need not be, because convexface 346 has to be visible whereas stem 345 need only be wide enough fordevice 200 to be secure for attachment to the hot metal or glass surfaceby means of attachment element 320. Convex face 346 of container 340houses the liquid crystal composition 230 and is transparent at least ina portion of the face 346 that covers the liquid crystal composition230. Alternatively, and less ideally, straight face 346 b of container340 b may be used, as seen in FIG. 20B.

[0087] As in the shape shown in FIG. 15A and 15B, container 340 in FIGS.16A and 16B is made of a heat conductive material. Unlike in FIGS. 15Aand 15B, in FIGS. 16A and 16B container 340 has a short cylindrical stem345 including a rear stem edge 345 a and has a convex face 346 that iscurved although typically not as much as a hemisphere. The liquidcrystal composition 230 is shaped in an outline of the letters “HOT” orin the background of such an outline. Liquid crystal composition 230 isembedded in the convex face 346 of the container 340 and is designed toturn red and remain red whenever the temperature of the hot surfaceexceeds a specified temperature.

[0088] Device 200 shown in FIGS. 16A, 16B, as with device 200 shown inFIG. 15, includes attachment element 320 that is made of a heatconductive material and has a hot surface attachment side 320 a and acontainer attachment side 320 b. Attachment element 320 is removablefrom and attachable to the metal or glass surface on the hot surfaceattachment side 320 a. The rear stem edge 345 a on container 340 is flatand attaches to the flat edge of container attachment side 320 b of theattachment element 320.

[0089] As in FIGS. 15A and 15B, in FIGS. 16A and 16B, device 200includes container 340 that is either a solid piece of heat transmittingplastic or any of a variety of transparent heat transmitting glasswaresuch as that sold under the name “Pyrex”. Likewise, convex face 346displays the letters “HOT” when the surface to which the heattransmission element 320 is attached is at a specified temperature, suchas a temperature above approximately 115 degrees Fahrenheit. Rear stemedge 345 a of container 340 attaches to either a magnet 320, which sinceit is metal transmits heat and is removably attachable to a hot metal orglass surface, or else it attaches to a detachable adhering plastic thatalso transmits heat and whose adhesive strength is sufficiently weakthat it is detachable yet sufficiently strong that it can adhere anobject of a decent amount of weight to a smooth metal or glass (or othersuitable) surface. An example of a heat transmitting plastic ispolyacetylene. 3M, the well known company in Minnesota, manufactures andsells adhesives that are used for temporarily attaching objects thathave significant weight to a surface.

[0090] As seen in FIG. 17, another alternative shape of device 200 isshown. In this embodiment there is an inner cylinder container 290, inthe shape of the hole of a doughnut, for housing the liquid crystalcomposition 230. Face 292 of inner cylinder container 290 ideally shouldbe convex for better viewing of the letters “HOT” (although face 292could less ideally also be straight and not convex) and is transparentat least in a portion of face 292 covering the liquid crystalcomposition 230. Inner cylinder container 290 is made of a heatconductive material capable of being transparent. As in FIGS. 15A, 15B,16A, 16B, in FIG. 17 the liquid crystal composition 230 is designed toturn red and remain red whenever the temperature of the hot surfaceexceeds a specified temperature. In this shape shown in FIG. 17, thereis an outer cylinder attachment element 280 made of a heat conductivematerial and in the shape of a doughnut having a flat rear wall (notshown) for attaching to the hot metal or glass surface. The inside wall289 of the outer cylinder attachment element 280 is attachable to theinner cylinder container 290 and the flat rear wall (not shown) ofattachment element 280 allows removable attachment of device 200 to ahot surface. Inner cylinder container 290 is also flat on its innercylinder container rear wall (not shown) and the inner cylindercontainer rear wall (not shown) is typically flush with the flat rearwall (not shown) of attachment element 280 in order to not impede thesmooth attachment of device 200 to a hot surface.

[0091] Each of the embodiments of device 200 depicted in FIGS. 15through 20 are versatile heat alert safety devices in that they arereadily attachable to and later detachable from any surface that may behot even after the source of the heat has been shut off. Such surfacescan include metal or glass and may include the metal or glass wall ofany heat-producing appliance such as the wall of an electric stove, gasstove, smoothtop stove, oven, toaster or a metal crock pot. The hotsurfaces to which device 200 can be attached need not be restricted tometal or glass but can be other surfaces that can receive a magnet ortemporarily adhering adhesives.

[0092] Two or more sides or walls of an appliance can sometimes get hotand the one side might not be suitable to have a heat alert safetydevice attached to it even though the same heat alert safety device ofthe present invention is made specifically for the other side of thesame appliance. For example, a heat alert safety device of the presentinvention for the top of an electric stove is not suitable forattachment to a side wall of that stove. Device 200 as depicted in FIGS.15A, 15B, FIG. 16A, FIG. 16B, FIG. 17, FIG. 19 and FIG. 20 can beapplied to any wall of such an appliance since it can be applied to anyhot surface. This application is especially useful for kitchen workerssurrounded by multiple ovens and/or hot counters—they can place device200 on each such hot surface.

[0093] Other surfaces that get hot and to which device 200 can beusefully applied besides food related appliances include radiator capslocated under the hood of a car or other vehicle, piping through whichhot steam flows, the surface of a curling iron, surfaces of a steampress and many others listed herein in the Objects and Advantages.

[0094] Accordingly, FIG. 18A shows a heat alert safety device 200designed specifically to be removably attachable to a rounded metal,glass or other hot surface, such as piping, that may be hot. In thisembodiment, the heat alert safety device 200 may be of the same shape asthe device 200 of FIG. 16 (or alternatively FIG. 15) except with respectto the shape of attachment element 420 of the device 200 of FIG. 18.Since the device 200 shown in FIG. 18 needs to be attached to a roundedsurface such as a pipe, the container 440 for housing the liquid crystalcomposition 230 has a short cylindrical stem 445 including a flat rearstem edge 445 a and container 440 has a convex face 446. Attachmentelement 420 has a concave hot surface attachment side 420 a and a flatcontainer attachment side 420, attachment element 420 is removable fromand attachable to the rounded hot surface on the hot surface attachmentside 420 a so as to allow the letters “HOT” to be visible. Flat rearstem edge 445 a attaches to the container attachment side 420 b ofattachment element 420. Alternatively and less ideally, as seen in FIG.18B, the concavity can also exist at the rear stem edge 445 a and at thecontainer attachment side 420 b of attachment element 420 (withidentical curvature).

[0095] Another feature of the present invention that enhances itsversatility is that device 200 can be positioned at a height suitablefor a small child and can be repositioned later at a different heightwhen the child is older and taller. In a family of many children ofdifferent ages and heights there would typically not be room on thewalls of an appliance for several different heat alert safety devices ofthe present invention. With the device 200 depicted in FIGS. 15-16,curved face 242 of FIG. 15 and convex face 346 of FIG. 16 are convex orrounded so that the letters “HOT” thereon may be read from a variety ofangles, depending upon the height (and angle of observation) of theobserver.

[0096] Another way in which the device 200 of the present invention canbe read from a variety of angles is that in one embodiment of device 200its angle of placement with respect to the observer is adjustable.Device 200 can be positioned at different angles from the viewer tomaximize the potential for observers, particularly children, to be ableto read the letters “HOT”. This is especially valuable when the heatalert device 200 is affixed to difficult to access surfaces that may behard to notice. It is critical that children actually be able to readthe letters “HOT” for the device to be effective.

[0097] In the embodiment shown in FIG. 19, device 200 can be positionedin a tiltably adjustable format so that the child needed to be warned ofthe hot surface can most easily read the letters “HOT” shown on convexface 522. At the edge at which stem 545 meets convex face 522 ofcontainer 540, well known rotation attachment means (not shown) allowsrotation of the convex face 522 with resistance through a discretenumber of positions. Convex face 522 can rotate on a frictional fit withstem 545, on threading exiting on stem 545 or by means of other wellknown rotation attachment techniques. As a result of such rotation, theangle that convex face 522 makes with the hot surface 599 can beadjusted to suit the height of the intended observer. Although FIG. 19has been presented with device being in the shape shown in FIG. 16A, theembodiment of FIG. 19 can also accommodate others shape of device 200such as that shown in FIG. 15.

[0098] When in this patent application, the heat warning symbol of thepresent invention is described with the phrase “the letters “HOT”, it isintended that this also include embodiments in which the letteringcomprising a word that means “HOT” in a foreign language is used insteadof the actual English letters “H”, “O” and “T”. Furthermore, other heatwarning symbols aside from the letters “HOT” are also within the scopeof the present invention—as one example, a picture of a flame.

[0099] In this patent application the phrase “exceeds 115 degreesFahrenheit” is intended to include embodiments in which the specifiedtemperature is a definite temperature other than 115 degrees Fahrenheitand in particular such other temperatures can fall between 112 and 116degrees Fahrenheit.

[0100] In general, it is to be understood that while the apparatus ofthis invention have been described and illustrated in detail, theabove-described embodiments are simply illustrative of the principles ofthe invention. It is to be understood also that various othermodifications and changes may be devised by those skilled in the artwhich will embody the principles of the invention and fall within thespirit and scope thereof. It is not desired to limit the invention tothe exact construction and operation shown and described. The spirit andscope of this invention are limited only by the spirit and scope of thefollowing claims.

What is claimed is:
 1. An improved plurality of heating elements of asmooth cooktop stove having a top surface that is smooth, each heatingelement comprising: a smooth area of glass on a smooth top surface ofthe stove that is subjected to a strong light source underneath saidsmooth area of glass, said light source generating heat in said smootharea of glass when said smooth area of glass absorbs light from thelight source, and a thermochromic composition embedded in a top surfaceof the smooth area of glass in an outline of a heat warning symbol, saidthermochromic composition designed to undergo and maintain a readilyperceptible color change whenever the temperature of the smooth area ofglass exceeds a specified temperature, the smooth area of glass in eachheating element forming a portion of the smooth top surface of thestove.
 2. The improved plurality of heating elements of claim 1, whereinthe heat warning symbol is the letters “HOT”.
 3. The device of claim 2,wherein the thermochromic composition is designed to turn red and remainred whenever the temperature of the smooth area of glass exceeds 115degrees Fahrenheit.
 4. The improved plurality of heating elements ofclaim 1, wherein heat warning symbol is a ring surrounding said heatingelement, which ring contains in an interrupted portion thereof anoutline of the letters “HOT”.
 5. The improved plurality of heatingelements of claim 4, wherein the thermochromic composition is designedto turn red and remain red whenever the temperature of the smooth areaof glass exceeds 115 degrees Fahrenheit.
 6. An improved plurality ofheating elements of a smooth cooktop stove having a top surface that issmooth, comprising: a smooth area of glass on a smooth top surface ofthe stove that absorbs heat from an electric heat source directlyunderneath said smooth area of glass and a thermochromic compositionembedded in a top surface of the smooth area of glass in an outline ofthe letters “HOT” or in an outline of a ring surrounding said heatingelement, which ring may contain in an interrupted portion thereof anoutline of the letters “HOT”, said thermochromic composition designed toundergo and maintain a readily perceptible color change whenever thetemperature of the smooth area of glass exceeds a specified temperature,the smooth area of glass in each heating element forming a portion ofthe smooth top surface of the stove.
 7. The improved plurality ofheating elements of claim 6, wherein the heat warning symbol is theletters “HOT”.
 8. The device of claim 7, wherein the thermochromiccomposition is designed to turn red and remain red whenever thetemperature of the smooth area of glass exceeds 115 degrees Fahrenheit.9. The improved plurality of heating elements of claim 6, wherein heatwarning symbol is a ring surrounding said heating element, which ringcontains in an interrupted portion thereof an outline of the letters“HOT”.
 10. The improved plurality of heating elements of claim 9,wherein the thermochromic composition is designed to turn red and remainred whenever the temperature of the smooth area of glass exceeds 115degrees Fahrenheit.
 11. A device for warning individuals of the hotsurface of a smooth cooktop stove, which stove has a top surface that issmooth and having a plurality of heating elements, which heatingelements are of the type wherein a smooth area of glass or metal issubjected to a heat source from underneath said area, comprising:thermochromic composition embedded in a top surface of a smooth area ofglass in an outline of a heat warning symbol, said thermochromiccomposition designed to undergo and maintain a readily perceptible colorchange whenever the temperature of the smooth area of glass exceeds aspecified temperature, the smooth area of glass in each heating elementforming a portion of the smooth top surface of the stove.
 12. The deviceof claim 11, wherein the heat warning symbol is the letters “HOT”. 13.The device of claim 12, wherein the thermochromic composition isdesigned to turn red and remain red whenever the temperature of thesmooth area of glass exceeds 115 degrees Fahrenheit.
 14. The device ofclaim 11, wherein heat warning symbol is a ring surrounding said heatingelement, which ring contains in an interrupted portion thereof anoutline of the letters “HOT”.
 15. The device claim 14, wherein thethermochromic composition is designed to turn red and remain redwhenever the temperature of the smooth area of glass exceeds 115 degreesFahrenheit.